Sit-ups are one of the most basic exercises we learn as we grow up. And while the basic sit-up can be done without any equipment whatsoever, we are limited in our ability to add variety and difficulty to the basic exercise. If you work out for any amount of time, you will eventually need a bench to get the maximum benefit from your workout. Fortunately, sit-up benches can be built in a variety of styles and from a variety of materials. This bench is built inexpensively from construction lumber and a small plywood panel.
Turn one of the triangular pieces you have cut from the 2-by-10 so the long diagonal edge is flat on the floor. As a check, the long upward-facing edge should be the same length as the plywood panel. If it is longer than the plywood, you have the wrong edge on the floor.
Butt the bottom of the large plywood panel against the top edge of the 2-by-10. Align the side of the 2-by-10 with the edge of the large panel.
Drill pilot holes for 2-inch screws through the top of the large panel into the edge of the triangular piece. Measuring from the end of the plywood panel closest to the floor, make your first hole about 12 inches from the end, then drill more holes, spaced about 3 inches apart, from there to the upper end of the panel.
Run a thick bead of glue along the edge of the 2-by-10 that you just drilled with holes.
Butt the bottom of the large plywood panel against the glued edge of the 2-by-10. Screw the two pieces together using 2-inch screws (13 screws total).
Repeat the previous steps with the other 2-by-10 triangle on the other long edge of the large panel. When finished, your assembly will look like a ramp.
Insert one of the 2-by-4s between the 2-by-10 triangles at the apex of the ramp. Drill three holes through the top of the ramp into one edge of the 2-by-4 -- one in the center of the ramp, and one hole about 3 inches on either side. Then drill two holes through one of the 2-by-10 triangles into the end of the 2-by-4; repeat on the other end of the 2-by-4.
Spread glue on the edges of the 2-by-4 with the holes, then reposition it and attach it to the ramp using screws. Use three 2-inch screws through the top of the ramp and four 4-inch screws through the 2-by-10s.
Repeat the process with the other 2-by-4, except put this one halfway down on the underside of the ramp.
Use 150-grit sandpaper to remove all the exposed rough edges.